The contributions of Pichia kudriavzevii EP1 to sourdough: Acid utilization, oligosaccharides and peptides production and aroma enhancement

Abstract

Previous studies have demonstrated that co-fermenting Pichia kudriavzevii EP1 (EP) and Fructilactobacillus sanfranciscensis can enhance the aroma of sourdough bread. This research aimed to examine the fermentation mechanism of EP compared to Saccharomyces cerevisiae (N) in sourdough and investigate the pathways involved in aroma production. Gas chromatography was used to analyze volatile organic compounds (VOCs) and their correlative essential metabolites. Metabolomics and proteomics were utilized to track changes in metabolic pathways and protein expression during fermentation. The findings revealed that EP fermentation resulted in a significant decrease in VOCs like 2-phenylethanol and octanoic acid, while showing a notable increase (384%) in hexanol production. Essential metabolites revealed reduced utilization of sugars and amino acids, and decreased generation of organic acids like lactic and acetic acid. Specifically, EP fermentation led to decreased levels of glucose-6-phosphate dehydrogenase, pyruvate kinase, NAD+, and NADH, while ATP showed a significant increase. Metabolomics and proteomics analyses highlighted reduced utilization of sugars and amino acids for VOCs production. Consequently, sourdough fermented with EP was rich in oligosaccharides and small peptide molecules. EP utilized organic acids not only to reduce sourdough acidity but also to generate acetyl-CoA. Acetyl-CoA served as energy sources for metabolic activities, such as catalyzing transformations between asparagine, aspartate, glutamate, and glutamine, and played a role in producing higher alcohols like hexanol to enhance sourdough aroma. These findings suggest that EP prefers acid utilization over sugars and amino acids, offering a potential strategy for enhancing sourdough aroma through individual or combined fermentations with other microbiotas.